This invention relates to galactosylated hydroxyalkyl polysaccharides and methods for preparation thereof.
Enzymatic methods for the preparation and modification of polysaccharides are known in the art. For example, U.S. Pat. No. 5,149,640 discloses a galactose transfer product prepared by a process of allowing a microorganism capable of producing a galactose transfer product to act on a combination of lactose or a galactose donor and a galactose receptor; and collecting the galactose transfer product produced.
U.S. Pat. No. 5,180,674 teaches a method and an apparatus for preparing saccharide compositions. The method is reiterative and comprises the following three steps: 1) a glycosyl transferase capable of transferring a preselected saccharide unit to an acceptor moiety is isolated by contacting the acceptor moiety with a mixture suspected of containing the glycosyl transferase under conditions effective to bind the acceptor moiety and glycosyl transferase and thereby isolate the glycosyl transferase. The acceptor moiety is a protein, a glycoprotein, a lipid, a glycolipid or a carbohydrate; 2) the isolated glycosyl transferase is then used to catalyze the bond between the acceptor moiety and the preselected saccharide unit; 3) steps (1) and (2) are repeated a plurality of times with the intermediate product obtained in the first iteration of the method being used as the acceptor moiety of the second iteration.
U.S. Pat. No. 4,957,860 discloses a method for producing oligosaccharides by the reaction between lactose and xcex2-galactosidase.
In U.S. Pat. No. 4,942,128 there is disclosed a method for producing microbial cellulose comprising inoculating a quantity of nutrient medium comprising a polysaccharide derivative such as carboxymethyl cellulose with a cellulose-producing microorganism. Cellulose resulting from this procedure is stated to be highly absorbent.
The preparation of galactosyl cyclodextrin by transgalactosylation has been reported by K. Koizumi et al., Carbohydrate Research, 278 (1995) 129-142.
Hydroxyalkyl polysaccharides, particularly hydroxyalkyl cellulose or cellulose derivatives and hydroxyalkyl guar or guar derivatives, are widely used as rheology modifiers, thickening agents and a variety of other applications. Methods to modify these materials by galactosylation, i.e., conversion of hydroxyl groups to galactosides, have been sought in order to modify the properties of the hydroxyalkyl polysaccharides and improve their performance.
A composition comprises galactosylated hydroxyalkyl polysaccharide wherein the hydroxyalkyl polysaccharide has a degree of substitution by galactose moieties bound to hydroxyl groups of the hydroxyalkyl polysaccharide by galactosidic bonds.
A process for preparing galactosylated hydroxyalkyl polysaccharide comprises:
a) providing at least one hydroxyalkyl polysaccharide; and
b) treating said hydroxyalkyl polysaccharide with a galactose donor in the presence of galactosidase enzyme for a time sufficient to cause a degree of substitution by galactose moieties at the hydroxyl groups of the hydroxyalkyl polysaccharide.